Internal combustion engines supplied by petrol are normally fitted with a butterfly valve which regulates the flow of air supplied to the cylinders. Typically, the butterfly valve has a valve body housing a valve seat engaged by a butterfly body which is engaged on a shaft in order to rotate between an open position and a closed position under the action of an electric actuator coupled to this shaft by means of a cascade of gears.
During normal operation, an internal combustion engine may become charged with static electricity which is generated essentially in the butterfly valve and in the air manifold as a result of the passage of a flow of dry air and in the petrol manifold as a result of the flow of petrol. It has been observed that the static electrical charge tends to be concentrated on the surface of the butterfly valve until the voltage generated reaches values (typically 30 000 to 60 000 V) such as to exceed the dielectric strength which separates it from a conductor body connected to earth disposed in the vicinity and thus to cause an electric arc (spark) which makes the two bodies equipotential again. This electric arc may be particularly harmful as it may damage the electronic circuits of the engine, may cause instantaneous malfunctions in the electronic circuits of the engine (typically by affecting the readings of the sensors and/or the transfer of data) and may be very dangerous in the presence of petrol fumes.
In order to remedy the drawbacks described above, U.S. Pat. No. 5,803,430-A1 proposes to insert a pair of resistors connected between the electrical terminals of the electric actuator and a wall of the intake duct at the location of the valve body. However, the solution proposed by U.S. Pat. No. 5,803,430-A1 is relatively costly because of the need to insert and connect two electrical components not normally included in the engine; experimental tests have shown, moreover, that this solution is not always able efficiently to discharge the static electricity accumulated in the butterfly valve; this solution also has an electric power that can be dissipated which is relatively modest (a characteristic which may pose problems from the point of view of complying with the constructional specifications normally imposed by manufacturers of engines for motor vehicles).